This invention relates to malolactic bacteria, and more particularly to a novel strain of Leuconostoc oenos capable of carrying out malolactic fermentation (MLF) in wines at relatively low temperatures and having relatively low pH values, i.e., high acidity.
Grapes grown in the northwestern United States and in the cooler wine-growing regions of Europe are generally lower in sugar and higher in acid than grapes grown in warmer climates. This is due to a number of factors, including the maturity of the grapes at harvest, the climate under which the grapes are grown, the cultivation practices utilized, soil conditions, fermentation procedures, etc. The low sugar content and high acidity of such grapes often results in the production of wines with harsh tastes.
Principal acids of the grape are tartaric and malic acid, and while the proportion of the total acidity contributed by malic acid is variable, when acidity is high, it may account for as much as half the total amount. Malolactic fermentation or MLF refers to the conversion of malic acid to lactic acid and carbon dioxide occurring in wine as the result of the metabolic activity of certain strains of lactic acid bacteria. The fermentation reduces the total acidity of the wine, stabilizes the wine biologically by assuring that MLF will not take place in the bottle, and further increases the flavor complexity of the wine. There are three genera of lactic acid bacteria that are principally associated with MLF in wines, and of these, the most predominant genus is Leuconostoc.
Pure culture inoculation of wine with Leuconostoc oenos offers several advantages to the wine maker. It enables the wine maker to stimulate MLF in musts, or wines, in a rapid and predictable manner, and provides assurance that a dependable bacterium is dominant in the fermentation. Bacteria such as L. oenos ML-34 and L. oenos PSU-1 are used commercially in locations such as California for such reasons. However, these organisms are not well suited to more northerly climes by reason of the low temperature conditions existing during wine production, and the low pH of the wines being processed, which render the bacteria relatively inactive.